1. Field of the Invention
This invention relates to hydrocarbon hydroprocessing catalysts, such as those utilized to catalyze the reaction of hydrogen with organo-sulfur, organo-metallic and particularly organo-nitrogen compounds. More particularly this invention is directed to a catalyst useful for the hydrodesulfurization of hydrocarbons, such as gas oils and residuum, and to a method for preparing such catalysts by employing a novel aqueous impregnating solution. The invention is especially directed to catalysts of high overall denitrogenation activity and stability.
2. Description of the Prior Art
In the refining of hydrocarbons, it is often necessary to convert a hydrocarbon oil fraction to different forms. Typically, particulate catalysts are utilized to promote desulfurization, denitrogenation or demetallization reactions when feedstocks such as gas oils or residuum are contacted with catalysts under conditions of elevated temperature and pressure and in the presence of hydrogen so that the sulfur components are converted to hydrogen sulfide, the nitrogen components to ammonia and the metals are deposited on the catalyst.
Hydroprocessing of hydrocarbon oils may be carried out with a catalyst containing Group VIB and Group VIII metals and phosphorus on a refractory oxide support. Compositions containing these and other elements have been previously investigated. For example, catalysts comprising a Group VIB metal, particularly molybdenum or tungsten, a Group VIII metal, particularly cobalt or nickel, and phosphorus on an alumina base have been disclosed in U.S. Pat. Nos. 3,755,196, 3,840,472 and 4,686,030. Such catalysts are very often prepared by impregnation, that is, the deposition of the active components on the support base by contact thereof with an aqueous solution containing the active components in dissolved form. U.S. Pat. No. 3,755,195, for example, describes impregnating media and methods for preparing catalysts using stabilized impregnating solutions consisting of molybdenum plus nickel or cobalt salts with phosphoric acid dissolved in an aqueous medium. U.S. Pat. No. 3,840,472 discloses another process for preparing a stable impregnating solution that includes dissolving a nickel or cobalt compound with an acid of phosphorus followed by subsequent dissolution of molybdenum oxide. U.S. Pat. No. 4,686,030 describes an impregnating solution containing dissolved Group VIII metals and dissolved molybdenum that is prepared by solubilizing molybdenum with either phosphoric acid, ammonium hydroxide or citric acid alone.
Although conventional catalysts are active and stable for hydrocarbon hydroprocessing reactions, catalysts of yet higher activities and stabilities are still being sought. Increasing the activity of a catalyst increases the rate at which a chemical reaction proceeds under given conditions, and increasing the stability of a catalyst increases its resistance to deactivation, that is, the useful life of the catalyst is extended. In general, as the activity of a catalyst is increased, the conditions required to produce a given end product, such as a hydrocarbon of given sulfur, nitrogen, and/or contaminant metals content, become more mild. Milder conditions require less energy to achieve the desired product, and catalyst life is extended due to such factors as lower coke formation or the deposition of less metals.